1. Field of the Invention
The present invention relates to mirrors generally and, more particularly, but not by way of limitation, to a novel mirror having lighted indicia.
2. Background Art
While the present invention is described, for illustrative purposes, as being applied to mirrors used in vehicles, it will be understood that it may be applied as well to any mirror with which it is desired to display lighted indicia.
One or more mirrors are used in virtually every vehicle to permit the operator of the vehicle to observe objects or persons behind or at the side of the vehicle. This is essential for providing the visual warnings necessary for safe operation of the vehicle. For example, using mirrors permits the operator of the vehicle to avoid striking such objects or persons when operating the vehicle in reverse or to avoid striking another vehicle when changing lanes on a roadway. Since the mirrors are frequently viewed by the operator, the mirrors offer convenient areas in which to provide information to the operator in a non-intrusive manner.
With the advent of advanced vehicle systems, such as side and/or rear collision warning systems, providing visual warning symbology in positions other than the standard instrument cluster or the "head up" display is required. For these systems to operate properly, it is vital that the warnings be located in the area that the operator is viewing at the instant the warning is required and generated. For instance, a side collision warning system must produce its visual warning icons and/or text in the side mirror, as it is expected, and encouraged that this is where the operator will be looking during a lane change maneuver. As a safety feature, it is imperative that the visual symbology produced be bright, even under full sunlight conditions, but that the visual symbology show no residual effect when turned off.
Some systems have been developed for providing lighted symbology through a mirror surface; however, some of these suffer from three major technical difficulties based on the half-silvering (or reduced silvering) technique used to allow the symbol light to pass through the mirror surface. First, since the mirror surface is half-silvered, or half-attenuating, in the area of the symbology, half the available light from the light emitting diodes (LEDs) behind the mirror is lost, producing a very weak signal that is not visible under all light conditions, such as direct sunlight striking the mirror surface. Second, and again due to the half-attenuating mirror coating, the symbol can be viewed when the LEDs are not operating, as the mirror surface is not longer fully reflective in this area. Third, the symbology cannot be changed once the mirror is produced.
Another known system uses LEDs behind an ordinary mirror, providing only about one percent transmission over the visible spectral region. The resulting signal is dim and not visible under bright sunlight conditions.
Another known system creates symbology by selectively removing a portion of mirror coating in the shape of the desired symbol and placing LEDs behind the area. The disadvantages of this approach are: (1) the symbols are visible when the LEDs are turned off and (2) once the symbol is created, there is no flexibility for change.
Yet another known system provides multiple layer thin film coatings on the rear surface of the mirror to create a narrow bandpass filter tuned to pass the precise frequency spectrum of light matching that of a chosen LED and reflecting all others. The process and calculations required for tuning the thickness of each layer to produce the desired result are well known. The calculations allow for the production of a bandpass filter in which one may choose both the central frequency and width of the passband. A light reflective mask that is essentially 100 percent attenuating to light is provided and an opening in the shape of a symbol to be displayed is cut in the mask. The mask is mechanically mounted to the coated rear surface of the mirror and LEDs having the chosen spectrum of light are placed behind the opening. This system provides a mirror having a selectively lightable symbol which is viewable in a wide range of light conditions but which is virtually invisible when not lighted. A drawback of this system is that, heretofore, it has been limited to a single color. A further drawback of this system is that it is not possible to selectively change what is displayed, for example, when it is desired to display different text in the same area of the mirror.
Accordingly, it is a principal object of the present invention to provide a mirror having lighted indicia visible in a wide range of ambient light conditions.
It is a further object of the invention to provide such a mirror in which the indicia are invisible or nearly so when the light source is turned off.
It is an additional object of the invention to provide such a mirror in which different indicia may be selectively displayed in a given area or areas of the mirror.
It is another object of the invention to provide such a mirror which can be economically manufactured.
It is yet a further object of the invention to provide such a mirror that has multicolor capability.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.